Emissions regulations worldwide emphasize reducing fine particulate matter emissions. It appears that fine particles are more strongly linked with adverse health effects than are large particles, and engines are predominant sources of fine particles. Indeed, changes in engine technology to reduce particle mass emissions has led to dramatic increases in the number of tiny particles (too small to constitute much mass) emitted. The nuclei mode particles range in diameter from 5-50 nanometers. They consist of a mix of sulfuric acid and partially burned fuel and lubricating oil. Most nuclei mode particles are not formed until the exhaust combustion products dilute and cool in the atmosphere, when the vapor phase precursors of nuclei mode particles are more likely to undergo gas to particle conversion.
In order to meet future emissions standards, future diesel engines probably will have to be fitted with sophisticated combustion control systems and, probably, aftertreatment systems including particle filters and traps. An effective exhaust particulate sensor can provide information to abet the reduction of particulate emissions from the engine and, consequently, to make traps and other aftertreatment devices more feasible. The particulate traps could be smaller or could regenerate less often, reducing the expense and the penalty on fuel economy.
It is also desirable to minimize oxides of nitrogen in engine emissions. However, it is well known that reducing particulate matter in engine exhaust can result in greater oxides of nitrogen and vice versa. Therefore, tradeoffs are necessary, and more information about the makeup of engine exhaust will assist in achieving optimal results.
Existing engine emission sensors monitor long term trends in overall engine emissions (1-10 seconds in duration) or integrate total emissions over a fixed test cycle. However, in many engines, one or two cylinders contribute a majority of the emissions with these peaks exceeding emissions standards. Testing by the applicants showed considerable real variation in engine emissions from cylinder to cylinder and from cycle to cycle. That effect is masked when averaged across all cylinders.
Therefore, this invention uses sensors to instantaneously monitor the behavior of individual cylinders or engine cycle behavior in order to measure compliance with current and future emissions regulations that are based on “not to exceed” limits rather than average levels. The information obtained from the sensors also can be used for engine control or maintenance. The information obtained from the sensors can be logged for use during normal maintenance periods, and also can be used to change engine parameters to reduce higher emissions from malfunctioning cylinders.